1. Field of the Invention
This invention relates to an apparatus for leading a physiological/psychological state of a person to a desired state, and, more particularly, to a brain wave frequency triggering apparatus which leads the brain wave of a person to a desired frequency band.
2. Description of the Related Art
It is known that brain wave of a human being have a close relation to his physiological/psychological state. When a person is in relaxed condition, alpha (.alpha.) waves (about 8 to 13 Hz) appear most in the brain. Beta (.beta.) waves (about 14 to 30 Hz) appears most when the person is in active condition, while theta (.theta.) waves (about 4 to 7 Hz) appear most when the person feels sleepy.
A drawing phenomenon in which brain wave frequency is synchronized to external signal frequency is seen on brain waves of a human being. If an external signal is supplied to a person for leading current brain wave to a desired frequency band in which the corresponding brain wave frequency appears most, the person can be led to desired physiological/psychological state.
There is a brain wave frequency leading apparatus which supplies a stimulation such as light and/or sound to a person in order to trigger particular brain wave frequency corresponding to .alpha. waves in the brain to relax the person by utilizing those mutual effects of the brain wave frequency and the physiological/psychological state, thus reducing his mental stress or intending his mental concentration.
In this brain wave leading apparatus, a brain wave signal of a person to be tested (hereinafter referred to as "subject"), which is detected by a sensor, is passed through a filter to be converted to an optical signal, and then this optical signal is feedback to the subject to lead the brain wave. To lead the brain wave of the subject to a desired frequency band, a weighted mean frequency of the brain wave of the subject at rest or a weighted mean frequency f.sub.0 at the time the brain wave is swept with a predetermined frequencies is obtained to compute a leading center frequency F suitable for brain wave leading, and the brain wave is triggered using only a signal included in a predetermined frequency band around this leading center frequency F.
In the above brain wave leading apparatus, however, the leading of the brain wave usually starts after the brain wave comes into an at-rest state or after the sweeping of the brain wave frequency is complete. If the brain wave frequency of the subject during brain wave leading becomes apart from the leading center frequency F, therefore, the brain wave leading efficiency tends to decrease. As a result, there are some cases which fail to lead the brain wave.